Add buildpack caching

Author: SimonErm

.github/workflows/main.yml

@@ -45,6 +45,8 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
       - id: build-image
         run: |
-         pack build imtrand -b paketo-community/rust -B paketobuildpacks/builder-jammy-base:latest
-         docker image tag imtrand ghcr.io/simonerm/imtrand:next
-         docker image push ghcr.io/simonerm/imtrand:next
+         pack build ghcr.io/simonerm/imtrand:next \
+         --buildpack paketo-community/rust \
+         --builder paketobuildpacks/builder-jammy-base:latest \
+         --cache-image ghcr.io/simonerm/imtrand-cache:next \
+         --publish